import java.util.Arrays;
import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: XMQ
 * Date: 2022-05-11
 * Time: 10:23
 */
//实例内部类的梳理
public class OutClass {
    public int data1 = 1;
    public int data2 = 2;
    public int data3 = 3;
    private static int data4 = 4;

    public static void outWay(){
        OutClass out = new OutClass();
        OutClass.InnerClass in = out.new InnerClass();
        System.out.println(in.data1);
        System.out.println("外部类的静态方法！");
    }
    public void func(){
        InnerClass in = new InnerClass();
        System.out.println(in.data1);
    }

    public class InnerClass{
        public int data5 = 5;
        private int data6 = 6;
        public static final int data7 = 7;  //实例内部类中不能定义静态的成员变量  如果非要定义要加上final
        public int data1 = 11111;
        public static final int data4 = 333;

        public InnerClass(){
            System.out.println("这是实例内部类的构造方法！");
        }
        public void inWay(){
            System.out.println("这是实例内部类的普通方法");
            System.out.println(data1);
            //也就是外部类有个引用在实例内部类中
            System.out.println("外部类同名成员变量"+OutClass.this.data1);
            System.out.println(data2);
            System.out.println(data3);
            System.out.println(data4);
            System.out.println(OutClass.data4);
            System.out.println(data5);
            System.out.println(data6);
        }

//        public static void innerWay(){
//            //内部类中不能定义静态的成员方法
//        }
    }
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        scan.close();
        //write your code here......
        double avg = 0;
        double sum = 0;
        int count = 0;
        while(scan.nextInt() >= 0){
            double ret = scan.nextInt();
            sum += ret;
            count++;
        }
        avg = sum/count;
        System.out.println(String.format("%.2f",avg));
        //求最小公倍数
//        Scanner console = new Scanner(System.in);
//        int m = console.nextInt();
//        int n = console.nextInt();
//        int result = getCM(m, n);
//        System.out.println(result);
    }

    public static int getCM(int m, int n){

        //write your code here......
        int a = m;
        int b = n;
        while(m%n != 0){
            int tmp = n;
            n = m % n;
            m = tmp;
        }
        return a*b/n;
    }
    public static void main1(String[] args) {

//        long[] array = new long[10];
//        array[0] = 9;
//        long sum = 0;
//        for(int i =0;i <array.length-1; i++){
//            array[i+1] = (long)(array[0]*Math.pow(10,i+1)+array[i]);
//            sum += array[i];
//        }
//        System.out.println(sum);
//        long count = 1;
//        sum = 0;
//        for(int i = 0;i < 10;i++){
//            count *= 10;
//            sum +=(count-1);
//        }
//        System.out.println(sum);

//        Scanner scanner = new Scanner(System.in);
//        String str = scanner.next();
//        String emailMatcher="[a-zA-Z0-9]+@[a-zA-Z0-9]+\\.[a-zA-Z0-9]+";
//        if(str.matches(emailMatcher)){
//            System.out.println("邮箱格式合法");
//        }else{
//            System.out.println("邮箱格式不合法");
//        }
//        int a = 10;
//        int b = 2;
//        System.out.println(Math.pow(a,b));
//        OutClass out = new OutClass();
//        OutClass.InnerClass in = out.new InnerClass();

//        OutClass.InnerClass in = new OutClass().new InnerClass();
//        in.inWay();
    }
}
